We take advantage of new 100-hour Spitzer/IRAC observations available for MACS0647-JD , a strongly lensed z \approx 11 galaxy candidate , to provide improved constraints on its physical properties .
Probing the physical properties of galaxies at z > 8 is challenging due to the inherent faintness of such sources and the limited wavelength coverage available .
Thanks to the high \approx 2-6 \times lensing magnification of the multiple images of MACS0647-JD , we can use the sensitive Spitzer/IRAC data to probe the rest-frame optical fluxes of MACS0647-JD and investigate its physical properties including the age and the stellar mass .
In deriving Spitzer/IRAC fluxes for MACS0647-JD , great care is taken in coping with the impact of three bright ( \approx 8-16 mag ) stars in our field to ensure robust results .
Assuming a constant star formation rate , the age , stellar mass , and rest-frame UV slope we estimate for MACS0647-JD based on a stack of the photometry are log _ { 10 } ( age/yr ) = 8.6 ^ { +0.1 } _ { -2.1 } , log _ { 10 } ( M _ { * } /M _ { \odot } ) = 9.1 ^ { +0.2 } _ { -1.4 } , and \beta = - 1.3 \pm 0.6 , respectively .
We compare our results with expectations from the EAGLE simulation and find that MACS0647-JD has properties consistent with corresponding to the most massive and rapidly star-forming galaxies in the simulation .
We also find that its radius , 105 \pm 28 pc , is a factor of \approx 2 smaller than the mean size in a separate simulation project DRAGONS .
Interestingly enough , the observed size is similar to the small sizes seen in very low-luminosity z \approx 6 -10 galaxies behind lensing clusters .